Sport shoes such as running, tennis or soccer shoes, as well as skates, ski boots and the like must fit tightly on the user's foot. During certain maneuvers, with a running shoe during heel strike and toe off, for example, the tightness of the fit needs to be greater than during other times when the forces transmitted between the foot and the ground via the shoe are not as severe. In the past, it was typical to tighten the shoe as much as possible, and physically bearable, to prevent or at least minimize relative movement of the foot in the shoe at times when maximum forces were transmitted between the foot and the shoe. As a practical matter, such a fit is excessively tight during most other times and quite frequently is uncomfortable, can lead to numbness and, in extreme cases, can even result in injuries. Thus, a compromise is frequently reached by tightening the shoe on the foot more than is necessary for the small forces that are applied and less than is desired to prevent relative movement of the foot in the shoe when large forces are applied. Consequently, the fit of such shoes is almost always other than what it should be.
This problem has been recognized in the past in connection with ski boots where the exerted forces are especially large and required tightness of the fit for extreme maneuvers is typically unbearable for any length of time. Thus, this inventor has developed dynamic fitting systems which temporarily increase the tightness of the fit of the boot on the foot in response to certain skiing maneuvers, for example, by constructing the ski boot so that the tightness of the fit of the boot, or of at least a portion of the boot increases in response to a forward lean of the skier. U.S. patent application Ser. No. 109,611, filed Jan. 4, 1980, entitled A SPORT SHOE WITH A DYNAMIC ADJUSTABLE CUFF ASSEMBLY, now U.S. Pat. No. 4,360,979, and U.S. patent application Ser. No. 274,031, filed June 15, 1981, entitled A DYNAMIC INTERNAL FITTING SYSTEM FOR A SPORT SHOE, now U.S. Pat. No. 4,338,735, describe such dynamic fitting systems.
In many respects, ski boots present a particular problem because it is one of their objectives to significantly limit the mobility of the user's ankle joint. For practical purposes, the skier's leg is movable in only a forward direction and even this movement is greatly limited when compared with the anatomical freedom of movement provided by the ankle joint. Further, ski boots are large, relatively bulky and have thick walls to provide the desired strength, rigidity and heat insulation. Consequently, there is ample space within which to build a system to tighten the boot in response to a particular movement, e.g. forward lean.
Up to now, little or no consideration has been given to the relative tightness of sport shoes particularly lightweight, highly mobile sport shoes such as running, tennis, soccer shoes and the like. The lightness of such sport shoes and the lack of an adequate analysis of the interaction between the sport shoe and the user's foot led to the practice of simply tightening the shoe to suit the user's taste, feel or preference. In some instances, the shoe might be too loose and not infrequently, slipped off the foot in a particularly strenuous maneuver such as a fall, a sudden change in direction when running and the like. This was considered an inevitable adjunct to participating in sports.
Upon closer analysis, however, it becomes apparent that there are distinct phases in the use of a sport shoe when forces applied by the foot to the shoe momentarily greatly exceed the normally encountered forces. In running, for example, upon toe off, that is when the runner plantarflexes his foot and puts his weight on the forefoot just prior to lifting the foot off the ground, there are significant forces which tend to push the foot in a rearward direction relative to the shoe. Conversely, during heel strike, that is when the foot contacts the ground at the end of a stride, there are significant forces generated by both the runner's weight and the deceleration of the foot which tend to move the foot in a forward direction relative to the shoe. Such movements may be relatively small, say in the order of no more than a few millimeters but they are present and, typically, they are repeated thousands of times during a single run. This can lead to discomfort, skin irritation from rubbing between the foot and the shoe and energy losses which, though small, are highly undesirable, particularly in competitive sports. The problem is magnified in contact type team sports where the forces can be significantly greater than those encountered during running, for example. Up to now, no solution to this problem was available.